Polymer powder and method of preparing the same

ABSTRACT

A powder composition suitable for use in laser sintering for printing a three-dimensional object. The powder composition includes a polyaryletherketone (PAEK) powder having a plurality of particles. The plurality of particles having a mean diameter of D50. The composition includes a plurality of carbon fibers having a mean length L50. L50 is greater than D50. The particles are substantially non-spherical. A portion of the carbon fiber is embedded into the particle via high intensity mixing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/446,470, filed Jan. 15, 2017, U.S. Provisional Application No.62/446,460, filed Jan. 15, 2017; U.S. Provisional Application No.62/446,462, filed Jan. 15, 2017; and U.S. Provisional Application No.62/446,464, filed Jan. 15, 2017. The contents of these priorapplications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure generally relates to additive manufacturingtechnology and techniques, and more specifically relates to a polyetherether ketone (“PEKK”) composition for use in selective laser sintering(“SLS” or “LS”), a method for preparing the PEKK composition, and amethod for additively manufacturing an object using the PEKK powder.

BACKGROUND

It is known to use additive manufacturing technology and techniques,together with fine polymer powders, to manufacture high-performanceproducts having applications in various industries (e.g., aerospace,industrial, medical, etc.).

SLS is an additive manufacturing technique that uses electromagneticradiation from a laser to selectively fuse a powder material typicallyhaving an average diameter of 25 to 150 μm into a desired 3-D object.The laser selectively fuses the powder material by scanningcross-sectional layers generated from a 3-D digital description of thedesired object onto the top layer of a bed of the powder material. Aftera cross-sectional layer is scanned, the powder bed is lowered by onelayer thickness in a z-axis direction, a new top layer of powdermaterial is applied to the powder bed, and the powder bed is rescanned.This process is repeated until the object is completed. When completed,the object is formed in a “cake” of unfused powder material. The formedobject is extracted from the cake. The powder material from the cake canbe recovered, sieved, and used in a subsequent SLS process.

PEKK powders are of particular interest in the SLS process becauseobjects that have been manufactured from PEKK powders are characterizedby a low flammability, good biocompatibility, and a high resistanceagainst hydrolysis and radiation. The thermal resistance at elevatedtemperatures as well as the chemical resistance distinguishes PEKKpowders from ordinary plastic powders.

An SLS machine typically pre-heats the PEKK powder disposed on thepowder bed to a temperature proximate to a melting point of the powder.Pre-heating the PEKK powder makes it easier for the laser to raise thetemperature of PEKK powder to a fusing point, and inhibits unwanteddistortions in formed objects during cooling. Techniques for pre-heatingof PEKK powders are discussed, for example, in U.S. patent applicationSer. No. 14/472,817, filed Aug. 29, 2014.

There is an ever-increasing need to manufacture objects via SLS usingPEKK powders with improved strengths (e.g., improved tensile strengthsin the z-axis direction), improved shape accuracies, and with fewer orno structural flaws (e.g., flaws due to improperly fused layers).Aspects of the present invention are directed to these and otherproblems.

SUMMARY

The needs set forth herein as well as further and other needs andadvantages are addressed by the present teachings, which illustratesolutions and advantages described below.

It is an objective of the present teachings to remedy the abovedrawbacks and issues associated with prior art selective laser sinteringmethods.

The present invention resides in one aspect in a powder compositionsuitable for use in laser sintering for printing a three-dimensionalobject. The powder composition includes a polyaryletherketone (PAEK)powder having a plurality of particles. The plurality of particleshaving a mean diameter of D50. The composition includes a plurality ofcarbon fibers having a mean length L50. L50 is greater than D50.

In yet further embodiments of the present invention the PAEK powdercomprises polyetherketoneketone (PEKK) particles.

It yet further embodiments of the present invention the PEKK particlesare substantially non-spherical.

In yet further embodiments of the present invention, at least a portionof the plurality of the carbon fibers are at least partially embedded inthe plurality of particles of the PAEK powder.

In yet further embodiments of the present invention, the D50 is between60 and 70 μm.

In yet further embodiments of the present invention, the L50 is between70 and 90 μm.

In yet further embodiments of the present invention, the D50 is between63 and 67 μm.

In yet further embodiments of the present invention, the carbon fiberaccounts for between 5% and 30% of the powder composition by weight.

In yet further embodiments of the present invention, the carbon fiberaccounts for 15% of the powder composition by weight.

In yet further embodiments of the present invention, the powdercomposition consists essentially of the PAEK powder and the carbonfiber.

In yet further embodiments of the present invention, the PAEK powderconsists essentially of PEKK.

In yet further embodiments of the present invention, the plurality ofparticles have a diameter between 20 and 150 μm.

The present invention resides in one aspect in a method of preparing apowder composition suitable for use in laser sintering for printing athree-dimensional object. The method includes the step of providing apolyaryletherketone (PAEK) powder having a plurality of particles, theplurality of particles having a mean diameter D50. The method furtherincludes the step of providing a plurality of carbon fibers having amedium length L50, the L50 being greater than D50. The method furtherincludes the step of mixing the PAEK powder with the carbon fibers toobtain the powder composition suitable for use in selective lasersintering.

In yet further embodiments of the present invention, the step ofproviding PAEK powder comprises the step of providing a plurality ofpolyetherketoneketone (PEKK) particles.

In yet a further embodiment of the present invention, the methodincludes the step of grinding a PEKK flake to form the PEKK particles,the PEKK particles being substantially non-spherical.

In yet a further embodiment of the present invention, the step of mixingcomprises mixing the PAEK powder with the carbon fiber in a highintensity mixer.

In yet a further embodiment of the present invention, the methodincludes the step of embedding a portion of the plurality of the carbonfibers into a portion of the plurality of particles of the PAEK powdervia the high intensity mixing.

In yet a further embodiment of the present invention, the methodincludes the step of mixing the PAEK powder with the carbon fiber in thehigh intensity mixer at a speed of greater than 500 rpm for at least oneminute.

In yet a further embodiment, the D50 is between 60 and 70 μm.

In yet a further embodiment of the present invention, the methodincludes the step of heat treating the PAEK powder before the grindingstep to evaporate any impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an LS machine in accordance with one embodiment ofthe present invention.

FIG. 2 is an image showing a magnified view of PEKK flake.

FIG. 3 is an image showing a magnified view of a plurality of PEKKparticles.

FIG. 4 is an image showing a magnified view of a plurality of PEKKparticles and a plurality of carbon fibers.

FIG. 5 is an image showing a magnified view of a plurality of PEKKparticles and a plurality of carbon fibers.

FIG. 6 is an image showing a portion of the image shown in FIG.

FIG. 7 is a chart showing a distribution of PEKK particles by particlediameter.

FIG. 8 is a chart showing a distribution of PEKK particles by particlediameter.

FIG. 9 is table showing data of a PEKK powder composition excludingcarbon fiber.

FIG. 10 is table showing data of a PEKK powder composition includingcarbon fiber.

DETAILED DESCRIPTION

The present disclosure describes aspects of the present invention withreference to the exemplary embodiments illustrated in the drawings;however, aspects of the present invention are not limited to theexemplary embodiments illustrated in the drawings. It will be apparentto those of ordinary skill in the art that aspects of the presentinvention include many more embodiments. Accordingly, aspects of thepresent invention are not to be restricted in light of the exemplaryembodiments illustrated in the drawings. It will also be apparent tothose of ordinary skill in the art that variations and modifications canbe made without departing from the true scope of the present disclosure.For example, in some instances, one or more features disclosed inconnection with one embodiment can be used alone or in combination withone or more features of one or more other embodiments.

The present invention is especially useful for preparing polymer powdersfor laser sintering. One such class of polymer powders isPolyaryletherketones (“PAEK”) polymers. PAEKs are of interest in the SLSprocess because parts that have been manufactured from PAEK powder orPAEK granulates are characterized by a low flammability, a goodbiocompatibility, and a high resistance against hydrolysis andradiation. The thermal resistance at elevated temperatures as well asthe chemical resistance distinguishes PAEK powders from ordinary plasticpowders. A PAEK polymer powder may be a powder from the group consistingof polyetheretherketone (“PEEK”), polyetherketoneketone (“PEKK”),polyetherketone (“PEK”), polyetheretherketoneketone (“PEEKK”) orpolyetherketoneetherketoneketone (“PEKEKK”).

PEKKs are well-known in the art and can be prepared using any suitablepolymerization technique, including the methods described in thefollowing patents, each of which is incorporated herein by reference inits entirety for all purposes: U.S. Pat. Nos. 3,065,205; 3,441,538;3,442,857; 3,516,966; 4,704,448; 4,816,556; and 6,177,518. PEKK polymersdiffer from the general class of PAEK polymers in that they ofteninclude, as repeating units, two different isomeric forms ofketone-ketone. These repeating units can be represented by the followingFormulas I and II:-A-C(═O)—B—C(═O)—  I-A-C(═O)-D-C(═O)—  II

where A is a p,p′-Ph-O-Ph-group, Ph is a phenylene radical, B isp-phenylene, and D is m-phenylene. The Formula I:Formula II isomerratio, commonly referred to as the T:I ratio, in the PEKK is selected soas to vary the total crystallinity of the polymer. The T:I ratio iscommonly varied from 50:50 to 90:10, and in some embodiments 60:40 to80:20. A higher T:I ratio such as, 80:20, provides a higher degree ofcrystallinity as compared to a lower T:I ratio, such as 60:40.

The crystal structure, polymorphism and morphology of homopolymers ofPEKK have been studied and have been reported in, for example, Cheng, Z.D. et al, “Polymorphism and crystal structure identification inpoly(aryl ether ketone ketone)s,” Macromol. Chem. Phys. 197, 185-213(1996), the disclosure of which is hereby incorporated by reference inits entirety. This article studied PEKK homopolymers having allpara-phenylene linkages [PEKK(T)], one meta-phenylene linkage [PEKK(I)]or alternating T and I isomers [PEKK(T/I)]. PEKK(T) and PEKK(T/I) showcrystalline polymorphism depending upon the crystallization conditionsand methods.

In PEKK(T), two crystalline forms, forms I and II, are observed. Form Ican be produced when samples are crystallized from melting at lowsupercoolings, while Form II is typically found via solvent-inducedcrystallization or by cold-crystallization from the glassy state atrelatively high supercooling. PEKK(I) possesses only one crystal unitcell which belongs to the same category as the Form I structure inPEKK(T). The c-axis dimension of the unit cell has been determined asthree phenylenes having a zig-zag conformation, with the meta-phenylenelying on the backbone plane. PEKK(T/I) shows crystalline forms I and II(as in the case of PEKK(T)) and also shows, under certain conditions, aform III.

Suitable PEKKs are available from several commercial sources undervarious brand names. For example, polyetherketoneketones are sold underthe brand name OXPEKK® polymers by Oxford Performance Materials, SouthWindsor, Conn. Polyetherketoneketone polymers are also manufactured andsupplied by Arkema. In addition to using polymers with a specific T:Iratio, mixtures of polyetherketoneketones may be employed.

The powders used in these applications are produced by a variety ofprocesses such as grinding, air milling, spray drying, freeze-drying, ordirect melt processing to fine powders. The heat treatment can beaccomplished before or after the powders are produced, but if treatedprior to forming the powders, the temperature of the powder formingprocess must be regulated to not significantly reduce the meltingtemperature or the quantity of the crystallinity formed in the heattreatment process.

In reference to FIG. 1, an LS system 10 in accordance with the presentinvention is illustrated. The system 10 includes a first chamber 20having an actuatable piston 24 deposed therein. A bed 22 is deposed atan end of the piston 24. It should be understood that the term bed mayrefer to the physical structure supported on the piston or the uppermostlayer of powder deposed thereon.

The temperature of the bed 22 can be variably controlled via acontroller 60 in communication with heating elements (not shown) in andor around the bed 22. Furthermore, the LS system 10 according to theinvention may include a heating device above the bed 22, which preheatsa newly applied powder layer up to a working temperature below atemperature at which the solidification of the powder material occurs.The heating device may be a radiative heating device (e.g., one or moreradiant heaters) which can introduce heat energy into the newly appliedpowder layer in a large area by emitting electromagnetic radiation.

A second chamber 30 is adjacent to the first chamber 20. The secondchamber 30 includes a table surface 32 disposed on an end of a piston 34deposed therein. A powder 36 for use in the LS system 10 is stored inthe second chamber 30 prior to the sintering step. It will be understoodto a person of ordinary skill in the art and familiar with thisdisclosure that while a specific embodiment of an LS system isdisclosed, the present invention is not limited and different known LSsystems may be employed in the practice of the present invention.

During operation of the LS system 10, a spreader 40 translates across atop surface of the first chamber 20, evenly distributing a layer ofpowder 36 across either the top surface of the bed 22, or the materialpreviously deposed on the bed 22. The LS system 10 preheats the powdermaterial 36 deposed on the bed 22 to a temperature proximate to amelting point of the powder. Typically, a layer of powder is spread tohave a thickness of 125 μm, however the thickness of the layer of powdercan be increased or decreased depending on the specific LS process andwithin the limits of the LS system.

A laser 50 and a scanning device 54 are deposed above the bed 22. Thelaser 50 transmits a beam 52 to the scanner 54, which then distributes alaser beam 56 across the layer of powder 36 deposed on the bed 22 inaccordance with a build data. The laser selectively fuses powderedmaterial by scanning cross-sections generated from a three-dimensionaldigital description of the part on the surface of the bed having a layerof the powdered material deposed thereon. The laser 50 and the scanner54 are in communication with the controller 60. After a cross-section isscanned, the bed 22 is lowered by one layer thickness (illustrated bythe downward arrow), a new layer of powdered material is deposed on thebed 22 via the spreader 40, and the bed 22 is rescanned by the laser.This process is repeated until a build 28 is completed. During thisprocess, the piston 34 in the second chamber is incrementally raised(illustrated by the upward arrow) to ensure that there is a sufficientsupply of powder 36.

In the method of preparing the powders in accordance with the presentinvention, raw PEKK flake is provided. The raw PEKK flake iscommercially available from companies such as Arkema, Inc. of King ofPrussia, Pa., and Cytec Industries Inc. of Woodland Park, N.J. The rawPEKK is typically swilled from a chemical reactor and then washed. Theraw PEKK is a non-powder material. That is, the raw PEKK is not in theform of a powder that can be used in the LS. As shown in FIG. 2, animage of raw PEKK flake is shown. The raw PEKK flake is in the form ofirregularly-shaped particles (e.g., particles that are vaguely round,elongated, flat, etc.) and has an appearance similar to that of RiceKrispies® cereal. The irregularly-shaped particles of the raw PEKK havegrain sizes that are orders of magnitude larger than 150 μm, forexample. The remainder of the raw PEKK can be in the form of a gel orgel-like form caused by an amount of liquid solvent remaining from theprocess of producing the raw PEKK.

After the step of providing the raw PEKK flake, a heat treatment step isperformed that involves placing the raw PEKK into a shallow pan andheating both within a convection oven. The temperature is ramped up to200° C. over an one-hour period. The temperature is held at 200° C. forseveral hours (e.g., 5 or 6 hours). The temperature is ramped up asecond time to 225° C. The temperature is held at 225° C. for a minimumof one hour and for preferably between one and four hours. Thetemperature is then ramped up a third time to 250° C. The temperature isheld at 250° C. for a minimum of one hour and for preferably between oneand four hours. The heat treatment step evaporates any remaining liquidsolvent, and causes at least substantially all of the raw PEKK to be inthe form of irregularly-shaped particles. The heat treatment step alsocauses some coalescence of the irregularly-shaped particles. However,the bulk density of the raw PEKK remains low after the heat treatmentstep.

After the heat-treating step, a cooling step is performed that involvespowering-off the convection oven heater and allowing the raw PEKK tocool naturally.

The heat-treatment process is the subject of copending U.S. patentapplication Ser. No. 15/872,478 filed on Jan. 16, 2018 by HexcelCorporation and titled “Polymer Powder and Method of Using the Same.”The disclosure of that reference is hereby incorporated by reference.

After the cooling step, a grinding step is performed that involvesgrinding the raw PEKK to form what will hereinafter be referred to asthe “PEKK powder.” The grinding step can be performed using knowngrinding techniques performed by companies such as Aveka, Inc. ofWoodbury, Minn. Upon completion of the grinding step, the particles ofthe PEKK powder are significantly smaller (i.e., several degrees ofmagnitude smaller) than the particles of the raw PEKK. The particles ofthe PEKK powder are more consistent and regular in shape as compared tothe particles of the raw PEKK; however, the particles of the PEKK powderare still irregularly-shaped in comparison to the spherical-shapedparticles of prior art PEKK powders that are pre-heated after grinding.

In accordance with the present invention, a person of ordinary skill inthe art and familiar with this disclosure will understand that thegrinding may also be referred to as pulverization, or jet milling. Inaddition, a person of ordinary skill in the art and familiar with thisdisclosure will understand that it may also be employed with otherpolymer powders, includes those in the PAEK family.

FIG. 3 shows an image showing magnified particles after the grindingprocess. In some embodiments of the present invention, the PEKK flake isground by a jet milling method. For example, Aveka CCE Technologiesbased in Cottage Grove, Minn., USA provides grinding and classificationservices. An air classifying mill is used that incorporates dense phasemicronization using turbulent, free jets in combination with highefficiency centrifugal air classification within a common housing. Thisprovides comminution by high probability particle-on-particle impact forbreakage and a high degree of particle dispersion for separation.

In accordance with the present invention, the raw PEKK flake is groundin a PAEK powder comprising a plurality of PEKK particles. The PEKKparticles range in size from less than 10 μm to about 200 μm. A personof ordinary skill in the art and familiar with this disclosure willunderstand that the particle size range will vary based on the type ofpolymer being milled and the specific parameters of the milling process.It is known in the art to reduce or eliminate particles having adiameter below a cut-off point, for example 20 μm, as it has been foundthat particles in this range may hinder use of the powder in the LSprocess or may degrade the mechanical properties of parts built via LStherefrom. For example, International Patent Application WO2014100320discloses such a method for preparing powders for use in selective lasersintering.

In reference to FIG. 3, an image captured using a microscope of aplurality of PEKK particles is shown. The resultant particles arenon-spherical and substantially angular. This is a result of the jetmilling process that performs particle comminution viaparticle-on-particle impact. The inventors have discovered that thesubstantial non-spherical PEKK particles perform better in the LSprocess. For example, the non-spherical particles are more easilydistributed on the bed table for the LS process and the non-sphericalparticles result in substantially stronger parts, particularly in theout of plane axis. The increased performance of non-spherical particlesis due in part to the increased ability for larger and smaller particlesto pack together enhancing the strength of the laser fusion.

In reference to FIGS. 7-8, two histograms are shown illustratingdifferential volume of a plurality of PEKK particles for use inaccordance with the present invention and in which fine particles havebeen removed in accordance with the above described method. Thedifferential volume was determined using the coulter counter method(following ISO 13319). The coulter method of sizing and countingparticles is based on measurable changes in electrical impedanceproduced by nonconductive particles suspended in an electrolyte. A smallopening (aperture) between electrodes is the sensing zone through whichsuspended particles pass. The coulter method enables the determinationof particle distribution by size according to particle mass relative tothe over mass of the sample or to particle count relative to the overallcount of particles in the sample. In reference to the information shownin FIGS. 7-8 and generally in this application, the term particlediameter is used to refer to the size of the particles. A person ofordinary skill in the art and familiar with this disclosure willunderstand that in context of the particle size, the term diameter doesnot indicate that the particles are spherical, but instead refers to thelargest size of the particle as determined via the coulter method. Asdiscussed above, the plurality of PEKK particles are highly angular andsubstantially non-spherical due to the particle-on-particle contactimpacts during the jet milling process.

In reference to FIG. 7, the chart 700 shows information relating to aplurality of PEKK particles associated with lot number 300393. Theplurality of particles have a mean diameter of 64.20 μm, and a mediandiameter of 61.34 μm. In reference to FIG. 8, the chart 800 showsinformation relating to a plurality of PEKK particles associated withlot number 7215. The plurality of particles has a mean diameter of 65.16μm and a median diameter of 62.85 μm. In some embodiments of the presentinvention, the PEKK powder has a mean diameter, also referred to as D50,between 60 μm and 70 μm. In yet other embodiments of the presentinvention, the PEKK powder has a mean diameter between 63 μm and 67 μm.

After the grinding step, another optional processing step is performedthat involves adding an amount of carbon fiber to the PEKK powder. Theaddition of the carbon fiber has the effect of reinforcing and/orstiffening the resulting object. Unlike prior art techniques thatinvolve use of carbon fiber with an average length L50 that is less thanthe average grain size d50 of the PEKK powder particles, the presentmethod involves use of carbon fiber with an average length L50 that islonger than the average grain size d50 of the PEKK powder particles. Insome embodiments, PEKK powder and carbon fibers can be selected suchthat d50<L50<d90. The carbon fiber and the PEKK powder can be combinedusing a heat shear process that involves combining the two componentsusing high speed, high torque mixing elements (e.g., a Henschel Mixer®).This has the effect of forcibly dispersing fiber clumps. If left intact,these clumps negatively impact both electrical behaviors and mechanicsof the mixture. The more commonly used tumbling blenders (e.g., V-typeblenders) lack the energy to disperse fibers correctly. It can beadvantageous to prepare large batches of the PEKK powder and carbonfiber mixture for the sake of reducing variability in the processes.

In accordance with one embodiment of the present invention carbon fiberavailable from Hexcel Corporation of Stamford, Conn., USA and sold underthe brand name HEXTOW® AS4 is employed. The carbon fiber is acontinuous, high strength, high strain, PAN based fiber. In thisembodiment, the carbon fiber has a filament diameter of approximately7.1 μm and is wound on a cardboard tube. It should be understood to aperson having ordinary skill in the art that different types and brandsof carbon fibers may be employed, and that the present invention is notspecifically limited in this regard.

The carbon fiber is milled prior to incorporation into the PEKK powderto achieve the desired carbon fiber length as determined by the averageL50. The carbon fiber is milled by a miller such as E&L Enterprises Inc.in Oakdale, Tenn., USA. For example, in one embodiment of the presentinvention, the mean carbon length, L50, is 77 μm. The minimum lengthmeasured is 38.15 μm, the maximum length measured is 453 μm, and thestandard deviation is 42.09 μm.

In accordance with the present invention, the milled carbon fiberincluded in the powder has a mean length L50 that is greater than themean diameter of the plurality of particles D50. In some embodiments,the L50 is greater than 70 μm. In some embodiments of the presentinvention, the L50 of the carbon fiber is between 70 μm and 90 μm. Inyet other embodiments of the present invention, the average fiber lengthL50 is between 70 μm and 80 μm.

A powder composition suitable for use in a selective laser sintering forprinting a three-dimensional object is prepared combining a PEKK powderwith the carbon fiber. In some embodiments of the present invention thecomposition includes 85% by weight of PEKK powder and 15% by weightcarbon fiber. It yet other embodiments of the present invention, theamount of carbon fiber is varied relative to the polymer powder toachieve composition for SLS. In some embodiments of the presentinvention, one or more additives are added to the matrix to affect theproperties of the SLS composition, for example, during the printingprocess or in the printed article. It will be understood to a person ofordinary skill in the art and familiar with this invention, that theratio of carbon to polymer may vary and the above examples are providedfor illustration purposes. The polyaryletherketone (PAEK) powder has aplurality of particles having a mean grain size D50. A plurality ofcarbon fibers have a mean length L50. L50 is greater than D50.

The plurality of carbon fibers and the plurality of PEKK particles aremixed in a high intensity mixer. This may include the Henschel FM 200high intensity mixer offered by Zeppelin. In the process of highintensity mixing the carbon fibers and PEKK particles are accelerated athigh speeds causing collisions between the fibers and the particlesthereby embedding the fibers into the PEKK particles. For example, acomposition in accordance with the present invention was prepared usinga high energy mixer (Zeppelin FM-200) that ran 7 minutes per batch(maximum 100 lbs fit in the mixer) and the slowest speed is 600 RPM. Ithas been discovered that embedding the carbon fiber into the particlesvia the high intensity mixing method results in a portion of the fiberin the particle and a portion of the fiber outside the particle. Thisconfiguration has been shown to significantly increase the mechanicalproperties of parts made from the composition powder using the LSmethod.

In reference to FIGS. 4-6, images 400, 500, 600 are provided showingmagnified views of a plurality of PEKK particles and a plurality ofcarbon fibers after completion of the high energy mixing. As shown inthe images, at least a portion of the plurality of the carbon fibers areat least partially embedded in the plurality of particles of the PAEKpowder and a least a portion of the carbon fiber is protrudingtherefrom. The images 400, 500, 600 also illustrate that the parties aresubstantially non-spherical and highly angular.

In reference to tables shown in FIGS. 9 and 10, a comparison of partsmade from a first composition consisting essentially of PEKK powder anda second composition consisting essentially of PEKK powder and carbonfiber prepared in accordance with the present invention is shown. Thepowders are sold under the names OXPEKK®-N and OXPEKK®-ESD, wherein Nincludes PEKK powder and ESD includes PEKK powder blended with carbonfiber. The comparison confirms that parts made with the carbon fibers inaccordance with the present invention are unequivocally stronger thanparts made from pure PEKK powder.

In reference to FIG. 9, Table 1 900 shows the properties of PEKK powdersold under the brand name OXPEKK®-N from Oxford Performance Materials,Inc. The left column, Cake Level, identifies the number of LS cyclesthat an OXPEKK®-N powder has been exposed to. Virgin refers to a powderthat has not been exposed to LS process, while Cake A has been exposedto 1 LS process, Cake B—2 LS process, etc. Each cake level was subjectedto an LS build process that manufactured test rods in the x-plane. Thetensile properties were determined pursuant to ASTM D638. The powder wasmanufactured in accordance with the above described method.Specifically, it consisted essentially of PEKK powder. The particleswere substantially non-spherical and the carbon fiber was mixed with thePEKK powder via high intensity mixing to partially embed the fiber intothe particles.

In reference to FIG. 10, Table 2 1000 shows the properties of ESD PEKKpowder sold under the brand name OXPEKK®-ESD from Oxford PerformanceMaterials, Inc. The left column, Cake Level, identifies the number of LScycles that an OXPEKK®-ESD powder has been exposed to. Virgin refers toa powder that has not been exposed to LS process, while Cake A has beenexposed to 1 LS process, Cake B—2 LS processes. Each ESD cake level wassubjected to an LS build process that manufactured test rods in thex-plane. The tensile properties were determined pursuant to ASTM D638.The powder was manufactured in accordance with the above describedmethod. Specifically, it consisted essentially of PEKK powder and carbonfiber in a ratio of 85/15 by weight. The D50 of the powder was between60 μm and 70 μm and the L50 of the powder was between 70 μm and 80 μm.The particles were substantially non-spherical and the carbon fiber wasmixed with the PEKK powder via high intensity mixing to partially embedthe fiber into the particles.

Another aspect of the invention is a PEKK powder manufactured accordingto the above-described method.

Another aspect of the invention is a method for additively manufacturingan object using a PEKK powder manufactured according to theabove-described method. The method involves the step of selective lasersintering the PEKK powder, and excludes any intentional pre-heating stepsuch as that typically performed using prior art techniques. Aside fromthe heating of the PEKK powder by the laser, the only other heating ofthe PEKK powder will be unintentional heating caused by movement ormanipulation of the PEKK powder.

What is claimed is:
 1. A powder composition comprising: apolyaryletherketone (PAEK) powder having a plurality of particles, theplurality of particles having a mean diameter D50 between 60 and 70 μm;a plurality of carbon fibers having a mean length L50; wherein L50 isgreater than D50, wherein the powder composition is suitable for use inlaser sintering for printing a three-dimensional object.
 2. The powdercomposition of claim 1, wherein the PAEK powder comprisespolyetherketoneketone (PEKK) particles.
 3. The powder composition ofclaim 2, wherein the PEKK particles are substantially non-spherical. 4.The powder composition of claim 3, wherein at least a portion of theplurality of the carbon fibers are at least partially embedded in theplurality of particles of the PAEK powder.
 5. The powder composition ofclaim 4, wherein the L50 is between D50 and 90 μm.
 6. The powdercomposition of claim 5, wherein the L50 is between 70 and 90 μm.
 7. Thepowder composition of claim 6, wherein the D50 is between 63 and 67 μm.8. The powder composition of claim 5, wherein the carbon fibers accountfor between 5% and 30% of the powder composition by weight.
 9. Thepowder composition of claim 8, wherein the carbon fibers account for 15%of the powder composition by weight.
 10. The powder composition of claim8, wherein the powder composition consists essentially of the PAEKpowder and the carbon fiber.
 11. The powder composition of claim 10,wherein the PAEK powder consists essentially of PEKK and the carbonfiber.
 12. The powder composition of claim 8, wherein the plurality ofparticles have a diameter between 20 and 150 μm.
 13. A method ofpreparing a powder composition suitable for use in laser sintering forprinting a three-dimensional object, the method including the steps of:providing a polyaryletherketone (PAEK) powder having a plurality ofparticles, the plurality of particles having a mean diameter D50 between60 and 70 μm; providing a plurality of carbon fibers having a mediumlength L50 between D50 and 90 μm; mixing the PAEK powder with the carbonfibers to obtain the powder composition suitable for use in selectivelaser sintering.
 14. The method of claim 13, wherein the step ofproviding PAEK powder comprises the step of providing a plurality ofpolyetherketoneketone (PEKK) particles.
 15. The method of claim 14,further comprising the step of: grinding a PEKK flake to form the PEKKparticles, the PEKK particles being substantially non-spherical.
 16. Themethod of claim 15, further comprising the step of mixing comprisesmixing the PAEK powder with the carbon fiber in a high intensity mixer.17. The method of claim 16 further comprising the step of: embedding aportion of the plurality of the carbon fibers into a portion of theplurality of particles of the PAEK powder via the high intensity mixing.18. The method of claim 16 further comprising the step of: mixing thePAEK powder with the carbon fiber in the high intensity mixer for anoperation speed of greater than 500 rpm for at least one minute.
 19. Thepowder composition of claim 18, wherein the D50 is between 63 and 67 μm.20. The method of claim of claim 15 further comprising the step of: heattreating the PAEK powder before the grinding step to evaporate anyimpurities.